This Non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 095147370, filed in Taiwan, Republic of China on Dec. 18, 2006, the entire contents of which are hereby incorporated by reference.
1. Field of Invention
The present invention relates to a luminescent device and a manufacturing method thereof, and more particularly to an electroluminescent device and a manufacturing method thereof.
2. Related Art
In recent years, the advances in electroluminescent technology push the material and manufacturing techniques of light emitting diode (LED) forward. Their applications range from indicators of computers or home appliances, backlight sources of liquid crystal displays, to traffic lights or vehicle lights. They may even be used as light sources of illumination. However, with increasing light emitting power, the LED also produces more heat. If such heat cannot be properly and effectively dissipated, the light emitting efficiency thereof will be lowered.
A conventional LED is formed by a dual attachment procedure. It involves the steps of growing an epitaxy layer on a temporary substrate, transferring the epitaxy layer to a glass substrate; removing the temporary substrate; coating a mirror reflective layer on the epitaxy layer; attaching the epitaxy layer on a permanent substrate; and removing the glass substrate.
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The epitaxy layer 14 is constituted by a p-type doped layer 141, a light emitting layer 142 and an n-type doped layer 143. In addition, a p-type electrode 151 is disposed on the p-type doped layer 141, and an n-type electrode 152 is disposed on the n-type doped layer 143. The material of the organic adhering layer 12 is generally PR, epoxy, polyimide, the coefficient of thermal conductivity of which is usually between 0.1 W/mk and 0.3 W/mk. Therefore, it is difficult to remove the heat generated from the LED 1. When the permanent substrate 11 is a metal, short circuits are likely to happen between the permanent substrate 11 and the epitaxy layer 14.
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The eutectic adhering layer 23 is formed by thermal pressing two metal layers 231, 232, thereby enhancing the bonding with the transparent conductive layer 24 and the metal reflective layer 22. However, the temperature required for the eutectic process is usually higher than 300˜400° C. This affects a certain effect on the epitaxy layer 25, which lowering its light emitting efficiency.
The present invention provides an electroluminescent device and a manufacturing method thereof that can provide a good heat dissipation path for removing heat generated therefrom, lower the temperature and raise the light emitting efficiency thereof.
An electroluminescent device according to the present invention includes a heat-conductive adhering layer, a heat-conductive substrate, a reflective layer, a light emitting diode (LED) element, a first contacting electrode and a second contacting electrode. The heat-conductive substrate is disposed on one side of the heat-conductive adhering layer. The reflective layer is formed on the other side of the heat-conductive adhering layer. The LED element is formed on the reflective layer and exposes a part of the reflective layer. The LED element includes a first semiconductor layer, a light emitting layer and a second semiconductor layer in sequence. The second semiconductor layer is in contact with the reflective layer. The first contacting electrode is electrically connected with the first semiconductor layer. The second contacting electrode is disposed on the exposed part of the reflective layer and electrically connected with the reflective layer.
Further, when the heat-conductive substrate is made by an electrically conductive material, the electroluminescent device can further include a heat-conductive insulating layer disposed between the heat-conductive adhering layer and the reflective layer or disposed between the heat-conductive substrate and the heat-conductive adhering layer so as to prevent short circuit between the LED element and the heat-conductive substrate.
A manufacturing method of an electroluminescent device according to the present invention includes the steps of forming a light emitting diode (LED) element on a plate, wherein the LED element includes a first semiconductor layer formed on the plate, a light emitting layer and a second semiconductor layer in sequence; forming a reflective layer on the LED element; forming a heat-conductive adhering layer on the reflective layer; attaching a heat-conductive substrate on the heat-conductive adhering layer; and removing the plate.
The manufacturing method of the electroluminescent device can further include a step of forming a heat-conductive insulating layer between the reflective layer and the heat-conductive adhering layer, or forming the heat-conductive insulating layer between the heat-conductive adhering layer and the heat-conductive substrate. This can prevent short circuit between the LED element and the heat-conductive substrate.
In the manufacturing method of the electroluminescent device, the material of the heat-conductive substrate includes Si, GaAs, GaP, SiC, BN, Al, AlN, Cu, or their combinations. The material of the heat-conductive adhering layer can be a bonding material, such as tin paste, tin-silver paste, silver paste, alloys, or a eutectic bonding material. The material of the heat-conductive insulating layer can be AlN, SiC or a high thermal conductivity insulating material.
As mentioned above, an electroluminescent device and a manufacturing method thereof according to the present invention utilize the heat-conductive adhering layer, the heat-conductive substrate and even the heat-conductive insulating layer with high coefficient of thermal conductivity to effectively dissipate heat generated from the LED element to the environment. It thereby raises the light emitting efficiency of the electroluminescent device.
The present invention will become more fully understood from the detailed description given herein below illustration only, and thus is not limitative of the present invention, and wherein:
The present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings, wherein the same references relate to the same elements.
This specification uses a first embodiment and a second embodiment to briefly explain an electroluminescent device and a manufacturing method thereof. Throughout this specification, the electroluminescent device is a light emitting diode (LED) as an example in these embodiments.
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It should be noted that the heat-conductive adhering layer 35 can also be formed on the heat-conductive substrate 36 by screen printing, spin coating, dispensing, or PVD process before it is attached onto the heat-conductive insulating layer 34. The sequence of these steps is not restricted by the present invention.
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In final, it is the step of forming the contacting electrodes 37. As shown in
In this embodiment, the above-mentioned steps can be performed under a temperature ranging between 25° C. and 300° C. Therefore, the present invention involves only low-temperature processes, and is less likely to affect the yield of the LED elements 32. It is worth mentioning that if the heat-conductive substrate 36 is made of an insulating material, no heat-conductive insulating layer 34 is required. Therefore, the step of forming the heat-conductive insulating layer 34 can be omitted.
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It should be noted that the heat-conductive adhering layer 44 can also be formed on the heat-conductive insulating layer 45 by screen printing, spin coating, dispensing, or PVD process before it is attached onto the reflective layer 43. The sequence of these steps is not restricted by the present invention.
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In this embodiment, removing part of the LED element 42 include the steps of forming a photoresist layer on the first semiconductor layer 421; exposing the photoresist layer by a light via a mask; removing part of the photoresist layer to form a patterned photoresist layer; removing a part of the first semiconductor layer 421, a part of the light emitting layer 422 and a part of the second semiconductor layer 423; and removing the patterned photoresist layer to expose part of the reflective layer 43.
In summary, an electroluminescent device and a manufacturing method thereof according to the present invention utilize the heat-conductive adhering layer, the heat-conductive substrate and even the heat-conductive insulating layer with high coefficient of thermal conductivity to effectively dissipate heat generated from the LED element to the environment. It thereby raises the light emitting efficiency of the electroluminescent device. In addition, since forming the heat-conductive adhering layer by screen printing, spin coating, dispensing or PVD process is a well-known and cheap method, and the production cost can be decreased while the yield can be increased. Moreover, forming the heat-conductive insulating layer between the heat-conductive substrate and the LED element can effectively prevent short circuit between them as well as enhance heat dissipation. Finally, utilizing the metal reflective layer with ohmic contact function to reflect light generated from the LED element can raise the external light extracting efficiency of the electroluminescent device.
Although the present invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments, will be apparent to persons skilled in the art. It is, therefore, contemplated that the appended claims will cover all modifications that fall within the true scope of the present invention.
Number | Date | Country | Kind |
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095147370 | Dec 2006 | TW | national |